China launched a food and drug safety crackdown on Wednesday, following an announcement that authorities detained managers from two companies linked to contaminated pet food that killed dogs and cats in North America.

State media, meanwhile, reported the country's disgraced former top drug regulator would go on trial this month on charges of taking bribes to approve untested medicine.

The ongoing revelations have shed a harsh light on China's notorious food and drug safety woes, sparking fears that exported products could contaminate food supplies abroad.

Few details were given about the detentions, which follow a U.S. Food and Drug Administration investigation sparked by the pet deaths and a recall of nearly 100 brands of pet food made with the tainted ingredients.

The FDA discovered melamine, a chemical used in plastics, fertilizers and flame retardants, in the pet food and traced the contaminated foodstuff to the Chinese companies.

In a notice on its Web site, China's government body responsible for overseeing food safety said investigators had focused on individuals at two companies blamed for the melamine tainting, and said local police had already brought charges. It did not name those under investigation or give other details.

"Relevant departments will deal strictly with the lawbreaking companies and those responsible according to the results of the investigation," the General Administration of Quality Supervision, Inspection and Quarantine said on its Web site.

China's State Council, or Cabinet, said the nationwide crackdown would compel companies to adopt "standards used in food-importing countries ... and test products which will be used to make animal feed or food for humans."

The government must "strengthen its investigations into protein products, especially melamine," the notice said.

That appeared to reflect concern over the impact of the scandals on China's exports of seafood, food additives and other such products, which compete strongly on price but which have been repeatedly singled out for contamination or low quality.

In one such recent case, Mississippi on Tuesday banned catfish from China after tests found ciprofloxacin and enrofloxacin, antibiotics which are banned for use in the United States.

Tainted drugs are also a serious problem. Recent reports have accused a Chinese company of selling diethylene glycol, a chemical cousin of antifreeze, that ended up in medicine that killed at least 51 people in Panama.

Zheng Xiaoyu, the former director of the State Food and Drug Administration, is accused of taking up to $780,000 in bribes to approve untested medicines, including an antibiotic that killed at least 10 patients.

Zheng was fired in 2005 and the official Xinhua News Agency said his trial will be held in mid-May.

The detained managers were identified as having worked for Xuzhou Anying Biologic Technology Development Co. Ltd. and Binzhou Futian Biology Technology Co. Ltd., both listed as having exported melamine-spiked rice protein and wheat gluten to the U.S.

U.S. inspectors said the tainted gluten was used to make pet food and caused the deaths of an unknown number of dogs and cats through liver failure.

Calls to office numbers at the companies rang unanswered on Wednesday. The mobile phones of managers at the companies were shut off.

A woman surnamed Cao at the Binzhou police in Shandong province said she could not comment because of the confidential nature of the case. Police on the provincial, city and county level in Jiangsu province where Anying Biologic is located said they had no information about the case.

The general administration statement said the companies had added melamine to the wheat gluten and rice protein in a bid to meet the contractual demand for the amount of protein in the products. It said doing so was against regulations.

However, the statement indicated the companies broke the law only when they mislabeled the exported products to avoid inspection.

The general administration said it ordered stepped-up inspections in the wake of its investigation, but that checks on 173 exporters in 11 provinces and cities had not turned up additional signs of melamine tainting after tests on 399 samples.

Additional checks for melamine were ordered on related products, such as processed meats and milk powder, but no contamination was found, it said.

The administration said it passed on those results to the FDA, officials from which were in China last week to meet government officials and visit companies. No details of the trip have been released, and it is not known if they are still in China.

"The U.S. side said it hoped for closer cooperation with the Chinese side in the area of boosting animal food safety," the notice said.

Melamine has no nutritional value but because it is nitrogen rich, it raises the nitrogen level of feed. That makes it appear to be higher in protein and, therefore, garnering a better price for the makers of feed for stock animals such as pigs, chickens, and fish, as well as companies that make prepared foods for household pets such as cats and dogs.

It is illegal to add melamine to food or animal feed in the U.S., although makers of the chemical and feed companies told The Associated Press last week the chemical was widely added to feed in China. They said they knew of no rules against the practice and were not aware that melamine could be harmful.

Xuzhou Anying managers have said they have no idea how the melamine got into the gluten, which they say was sourced from other firms and sold to a third company that exported it to the U.S.

However, suspicions were raised when the company was found to have posted an advertisement on the Web site of an online market in March seeking to buy melamine.

U.S. officials say they don't believe melamine to be harmful to humans, but say they have too little data to determine how it reacts with other substances.